This invention relates to an insoluble electrode device which is used for electrolytically treating a surface of a metallic material such as a metal plate, a metal strip, a metal tape and a metal foil; more particularly to an insoluble electrode device of a novel structure which is used, for example, when a surface of a metal strip is continuously subjected to a cathodic surface treatment such as electroplating and electrolytic chromate treatment, or an anodic surface treatment such as anodizing, and capable of supplying a fresh electrolyte solution constantly as a substantially uniform liquid flow to a space defined between the metal strip to be treated and the insoluble electrode as a counter electrode, whereby to enable high quality surface treatment of the metal strip. This invention particularly relates to an insoluble electrode device of a novel structure which can supply a fresh electrolyte solution constantly throughout the space between the electrodes which is defined by the metal strip to be treated and the insoluble electrode device as a counter electrode, and also can control the liquid flow of the electrolyte solution flowing through said space between the electrodes to minimize nonuniformity in the liquid flow of the electrolyte solution, whereby high quality surface treatment of the metal strip to be treated can be achieved.
When a metal strip is subjected to a surface treatment such as electroplating, for example, an anode is disposed to oppose a part of the metal strip immersed in an electrolyte solution, and the metal strip is weaved through the electrolyte solution to effect electrolytic treatment using the metal strip as a cathode.
An embodiment of the prior art will be described referring to the schematic drawing shown in FIG. 7. In FIG. 7, the numeral 1 shows a processing tank which is filled with a predetermined electrolyte solution 2. The numeral 3 shows a metal strip to be subjected to surface treatment, which is fed from outside of the tank into the electrolyte solution and runs through the electrolyte solution in the direction shown with an arrow P or in the opposite direction. The numerals 3a and 3b each show a guide roller, and 4 shows an anode which is disposed to oppose the part of the metal strip immersed in the electrolyte solution with a predetermined space there between.
Anodes of various shapes and materials have been proposed and can be exemplified by an insoluble electrode comprising a mesh or mesh plate, a perforated plate or a simple flat plate made of an insoluble metal, such as titanium, niobium and tantalum, having a coating of an active substance such as platinum or iridium oxide on the surface. An embodiment of such an insoluble electrode is shown in FIG. 8 by a perspective view. In FIG. 8, 4a shows a mesh composed of an insoluble metal and an active substance. FIG. 9 also shows another embodiment of a mesh electrode plate, by a side view, having a frame 4b surrounding the mesh electrode plate as shown in FIG. 8 for retaining the shape thereof and further a bus bar 4c on the back for achieving uniform power supply.
In such as electrolytic treatment, an effort has been made to bring the metal strip to be treated into constant contact with a fresh electrolyte solution, by supplying continuously the electrolyte solution into a processing tank and discharging continuously the solution from the tank. For example, there have been adopted various systems such as a system where there is provided, at the lower portion of a processing tank, a means for supplying an electrolyte solution (not shown in the drawing) from which means an electrolyte solution is supplied into the space between the electrodes and there is provided, at the upper portion of the tank, a means for discharging the solution (not shown either) from which the electrolyte solution is discharged, and a system where, in contrast to the above-mentioned system, a means for supplying the electrolyte solution is provided at the upper portion of the processing tank and a means for discharging the electrolyte solution at the lower portion of the tank. These prior art methods are to supply uniform and regular flow of a fresh electrolyte solution constantly or continuously over the whole space between the electrodes.
However, when electrolytic treatment is conducted using such a device as shown in FIG. 7, the electrolyte solution present in the space between the electrodes defined by the anode 4 and the metal strip 3 is either in a static state or in a state of natural convection or floating with the supply or discharge of the electrolyte solution to or from the tank, and there are irregularity and nonuniformity in the liquid flow of the electrolyte solution flowing through the space between the electrodes.
Therefore, the state of contact between the surface of the metal strip 3 to be surface-treated and the electrolyte solution cannot be said to be uniform over the whole surface to be treated. Accordingly, it cannot be said that the surface treatment of the metal strip 3 is carried on in a uniform state over the whole surface to be treated.
For such reasons, a measure has been taken to force the electrolyte solution in the space between the electrodes to be stirred or a fresh electrolyte solution to be supplied from the top or the bottom to this space to bring a fresh electrolyte solution into contact with the metal strip over the whole surface to be treated as completely as possible.
Nevertheless, the electrolyte solution to be brought into contact with the metal strip 3 remains as turbulence to show nonuniform liquid flow even if such measure has been taken, and thus it cannot be said that the surface treatment of the metal strip 3 can be carried out in a completely uniform state.